You can give a name to the cell which contains the subtotal (i.e. : toto
Menu : Insert Name Define..
Then in your code you can refer it with its nam
in VBA : Me.Range("toto").valu
in Excel formula : =IF(toto=0,"-","OK"

If you want to format a cell, you can use the "Conditional Formatting", it's quicker than VBA macr
Menu : Format Conditional Formatting..